This invention relates to the field of dual fuel systems for vehicles with internal combustion engines, and in particular vehicles with engines designed to use gasoline as their primary fuel wherein an alternate fuel system can be added to enable use of an alternate fuel by switching back and forth between gasoline and the alternate fuel.
Prior art devices of this kind of which the inventor is aware include those described in the following United States patents.
U.S. Pat. No. 5,228,423 discloses a dual fuel engine which uses liquid fuel such as gasoline or gaseous fuel such as compressed natural gas, wherein separate intake passages into the combustion chamber of each cylinder and separate fuel supply devices are provided for the gaseous fuel and for the liquid fuel. Both intake passages are provided with intake valves, and both intake valves are actuated when the liquid fuel is used but substantially only one of the intake valves is actuated when the gaseous fuel is used.
U.S. Pat. No. 4,878,475 discloses a dual fuel system for internal combustion engines, one fuel such as propane to start the engine, to operate it at idle speed and to supplement the other fuel during acceleration, and the second such as gasoline to operate the engine at its normal working speed. Vacuum controlled valves deliver the one fuel such as propane to the carburetor. The primary fuel such as gasoline is delivered to the carburetor by the usual fuel pump.
U.S. Pat. No. 4,606,322 discloses a dual fuel control and supply system for internal combustion engines such as diesel, but not necessarily confined to diesel engines, an injector pump to deliver the principal liquid fuel under pressure to the cylinders, an electronic control unit, and an electrically controllable variable flow regulator to receive a gaseous alternative fuel and deliver controlled quantities to the cylinders as signalled by the electronic control unit.
U.S. Pat. No. 4,594,201 discloses a multi-fuel system for internal combustion engines, comprising a non-venturi type of carburetor having a metered inlet and means for controlling the pressure of each fuel in accordance with the stoichiometric ratio of that fuel to assure proper fuel/air ratio is delivered to the mixing chamber of the carburetor without requiring any change in either the carburetor or engine when a different fuel is used.
U.S. Pat. No. 4,576,137 discloses a gas and a diesel dual fuel engine, wherein the engine has an electronic governor circuit adapted to receive both a speed signal representing the actual speed of the engine and a set speed signal representing a predetermined command speed of the engine, electric actuators to actuate a diesel fuel injection pump and a gaseous fuel regulating valve in response to the signal from the electronic governor circuit, with a switching control circuit to switch operation between diesel fuel and gaseous fuel.
U.S. Pat. No. 4,531,497 discloses a natural gas adaptor system for automobiles which normally run on gasoline, including a compressor driven by the vehicle's engine to compress low pressure natural gas up to a higher pressure, and an air mixing delivery system for delivering the compressed natural gas to the carburetor.
U.S. Pat. No. 4,354,477 discloses a multi-fuel carburetor with a rotary mixing valve which has multiple vanes to control the flow of main and secondary fuels into a mixing chamber to momentarily increase the octane rating of the fuel charge during acceleration, such as by mixing in a quantity of alcohol with gasoline in a predetermined ratio, for example as 1 part alcohol to 10 parts gasoline.
U.S. Pat. No. 4,031,864 discloses a multiple fuel supply system for an internal combustion engine wherein phase separation of a gasoline-methanol blend in a single tank is induces by adding a minor amount of water sufficient to guarantee separation into an upper gasoline phase and a lower methanol-water phase. Separate fuel pickups and separate level indicators are provided for each phase. Either gasoline or methanol can be supplied to the engine by the vehicle's fuel delivery system.
U.S. Pat. No. 3,659,574 discloses a natural gas powered engine having a dual fuel feed apparatus and control whereby the engine can operate on both natural gas and gasoline. Two carburetors are mounted in parallel at the intake manifold and a switch mechanism is provided to switch between natural gas from one carburetor and gasoline from the other.